An accumulator for strip material built according to U.S. Pat. No. 3,310,255 has solved the problem of continuously feeding modern fast steel strip processing lines where previously multiple-pulley looping towers did not give enough time for joining the next strip being, as it were, only a small fraction of the capacity of said accumulator. The high storage capacity in that relatively compact accumulator is explained by its geometry: the strip is stored in form of two superposed, individually supported spiral coils, one right- and the other left-hand wound, the two joined together into one continuous length at their inner wraps, so that the strip enters the first coil tangentially, through a pair of pinch rolls, from outside, and it leaves from the second coil in a similar way.
This accumulator has applications also in other branches of strip forming of which said patent shows two: such accumulator employed for feeding a continuous length of hot-rolled strip into a multi-stand tandem cold rolling mill without slowing down for butt-welding each new coil (FIG. 6) and its use in connection with a single-stand cold rolling mill arranged for a multipass one-way operation, the strip having been welded into a closed loop (FIG. 7 of that patent).
All of the above-listed and all known applications of accumulators, whether the herein referred to accumulator disclosed in U.S. Pat. No. 3,310,255, or the multiple traveling pulley accumulators, attack the problem of continuously feeding processing lines whose operation either must not be interrupted, such as galvanizing or annealing lines, or where equipment could be more fully utilized if operated without interruptions at the end of each coil, to butt-weld the following coil, e.g. rolling mill. Applicant has discovered, and is disclosing hereinafter, an entirely different application of variable capacity accumulators that offers substantial economic advantages in producing and processing metallic and nonmetallic strip material that can be treated in continuous lengths. This application is, however, limited to the use of large capacity strip accumulators, either of the above described or another type.
The application consists in using such variable capacity accumulator as recipient of the whole strip output of one production or processing line, followed by storing such strip material if necessary, and finally feeding it into the following processing line at such time and at such velocity as that line requires, or for final winding into coils or cutting up into sheets and packing, after the last processing operation.
The consequences of the present discovery can only be appreciated when compared with the one and only method now universally used in the strip and sheet producing industry where, e.g. in the steel industry, hot-rolled (pre-rolled) strip is delivered in coils to the processing works and the operations such as: (1) pickling, (2) cold rolling, (3) annealing and temper rolling (4) galvanizing or aluminum coating, plastic coating etc are each followed by winding such strip into coils, including of course cutting it at the end of the coil, then tying the coil with steel straps securely to prevent unwinding in transport, followed by loading the coils on cars or conveyors to transport them to intermediate storage. Then lifting the coils again by crane or lift truck and depositing in cars or using conveyors to deliver them to the entry end of the following processing line where they are placed one by one on a pay-off reel and joined by welding to the following coil end the moment the preceding coil is unwound to the end.
Steady progress in the last three decades has led to providing equipment that can produce and handle heavier and heavier coils in order to reduce the number of times the coils must be welded to obtain a continuous length. At the present moment coils weighing 40 to 50 tons each seem to be the limit and one can imagine how securely such coil must be strapped for handling and transportation. Loosening of the straps could lead to serious accidents.
U.S. Pat. No. 4,152,919 illustrates the point. The patent discloses strip handling equipment to and from a multistand cold-rolling mill for aluminum strips. The equipment consists of heavy conveyors, lifing equipment to transfer the coils from the conveyors and placing them on multifloor shelves with similar equipment to take them off the shelves on the other side and huge five-coil cars delivering the coils from the hot-rolling mill. The above-described system is represented as substantial improvement over prior art which is said to consist of cranes and lift trucks only. This patent further emphasizes the large storage areas needed to store the coils in production and the complications of coil handling.
By comparison, solving the same material handling problem according to the present invention by leading endless lengths of strip from one operation to the next one without the steps of winding them into coils, requires no handling equipment and no labor. It also requires a small fraction of the storage space because such accumulators can be built for huge capacities concentrated in small areas.